The blades have a diagonal key-way in each. This forms 'X' when they are assembled. A diamond guide is located within these key-ways. The pair of blades with the diamond-guide which has an elongated hole in position between the blades is assembled in a carrier where they are held by guide pin. This pin in Conjunction with the elongated hole in the diamond determines the float of the blades in operation. The carrier is controlled in its longitudinal movement by means of carrier pin which is positioned between the Adjuster and lock-ring. When this assembly of rings is rotated along the micrometer threads on the shank body, carrier responds by moving the diamond guide in its key-ways thus expanding or retracting the blades.